First, use the equation for circumference:
c= 2πr
now plug in what you know:
c= 2π(4.5)
c= 9π
So if you divide 78 by six you get 13. 78/6=13
So we want x minus 6 to equal thirteen we have to make x a number that will equal 13 when we subtract 6. So we can just add 13+6 to get 19. And 19-6=13. So x=19, does that make sense?
Multiply the 2nd equation by -3 to get -3x-12y = -48.